It must have been the blocking missing,

I didn't see you have a $chan->blocking(0/1), or if that is the type of blocking you are talking about.

If you google for "Net::SSH2 timeout" you will find it has been tricky to get timeouts to work. The latest module has a few lines where timeouts can be set

 connect ( handle | host [, port [, Timeout => secs ]] )
[download]

and

 poll ( timeout, arrayref of hashes )  #probably the timeout you want
[download]

You might want to look at Net::SSH2 Command Timeout Before Completion for other modules that handle the timeouts better.